Components found inside optical devices such as optical transmitters, detectors, optical amplifiers and repeaters may be susceptible to environmental contaminates and/or residual assembly organics such as resins or fluxes which can result in galvanic corrosion and other failure modes which cause the optical device to no longer operate in an acceptable manner. Thus, the interior region of the optical device may be either evacuated or filled with an inert element such as nitrogen. Typically, the device housings are then hermetically sealed. However, a problem exists as to how the optical signal will penetrate the housing while maintaining hermeticity and without unacceptable degradation in the transmission properties of the optical signal.
An example of an optical device in which this problem is particularly severe is an undersea optical repeater. Optical repeaters are used to provide amplification and/or other signal processing to optical signals traveling in an undersea optical transmission cable. In a typical optical repeater, the optical fiber or fibers carrying the optical signals, which are located within the transmission cable, enter the repeater and are coupled through at least one amplifier and various components, such as optical couplers and decouplers, before exiting the repeater. Since the repeaters are subject to harsh undersea environmental conditions, they are housed in a sealed structure that protects the repeaters from environmental damage. Accordingly, it is particularly important that the optical fibers enter the repeater in a hermetically sealed manner.
Typically, the coupling ends of optical fibers are provided within a ferrule, which is then hermetically fixed by soldering, welding or epoxy into a passage into the optical device. The ferrule, which is used because the optical fibers are flexible and have a very small diameter, holds the optical fiber at the desired location to provide proper alignment between the optical device and an end of the optical fiber. The ferrule is positioned within an orifice of the optical device and mounted thereto so that an end of the fiber is positioned proximate to and aligned with the optical device.
While currently available ferrules generally accept only a single optical fiber, there is growing need for multifiber ferrules that can form a hermetic seal with each of the individual optical fibers that are contained in the ferrule. For example, in optical transmission systems such as an undersea transmission system the transmission cable typically contains two or more optical fibers since a fiber pair is required to provide bidirectional communication. Each of these optical fibers therefore must enter the undersea optical repeater in a hermetic manner.
Accordingly, it would be desirable to provide a ferrule that forms a hermetic seal with two or more optical fibers.